1.生长发育特点　玉米抽雄以后 ,开始进入开花、授粉、受精以及籽粒建成为中心的生殖生长阶段。这个时期叶面积系数达到最大值 ,以后逐步下降 ,根系开始衰亡。吐丝期是决定粒数最关键的时期 ,进入粒期以后是决定粒重的重要时期。亩产 50 0千克玉米 ,吐丝期叶面积系数在 4 .5以 1. Growth and development characteristics Corn tasseled later, began to flowering, pollination, fertilization and grain into the center of the reproductive growth stage. The leaf area coefficient reached its maximum at this period, then decreased gradually and the root system began to decline. The silking period is the most critical period for determining the grain number. After entering the grain period, it is an important period for determining the grain weight. Acres yield 50 0 kg of corn, leaf area at silking stage at 4.5